package ip;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * 获取本机外网IP地址
 * 思想是访问网站http://checkip.dyndns.org/，得到返回的文本后解析出本机在外网的IP地址
 * @author Administrator
 *
 */
public class ExternalIpAddressFetcher {

	// 外网IP提供者的网址
	private final String externalIpProviderUrl;

	// 本机外网IP地址
	private String myExternalIpAddress;

	public ExternalIpAddressFetcher(String externalIpProviderUrl) {
		this.externalIpProviderUrl = externalIpProviderUrl;

		String returnedhtml = fetchExternalIpProviderHTML(externalIpProviderUrl);

		parse(returnedhtml);
	}

	/**
	 * 从外网提供者处获得包含本机外网地址的字符串
	 * 从http://checkip.dyndns.org返回的字符串如下
	 * <html><head><title>Current IP Check</title></head><body>Current IP Address: 123.147.226.222</body></html>
	 * @param externalIpProviderUrl
	 * @return
	 */
	private String fetchExternalIpProviderHTML(String externalIpProviderUrl) {
		// 输入流
		InputStream in = null;

		// 到外网提供者的Http连接
		HttpURLConnection httpConn = null;

		try {
			// 打开连接
			URL url = new URL(externalIpProviderUrl);
			httpConn = (HttpURLConnection) url.openConnection();

			// 连接设置
			HttpURLConnection.setFollowRedirects(true);
			httpConn.setRequestMethod("GET");
			httpConn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows 2000)");

			// 获取连接的输入流
			in = httpConn.getInputStream();
			byte[] bytes = new byte[1024];// 此大小可根据实际情况调整

			// 读取到数组中
			int offset = 0;
			int numRead = 0;
			while (offset < bytes.length && (numRead = in.read(bytes, offset, bytes.length - offset)) >= 0) {
				offset += numRead;
			}

			// 将字节转化为为UTF-8的字符串        
			String receivedString = new String(bytes, "UTF-8");

			// 返回
			return receivedString;
		}
		catch (MalformedURLException e) {
			e.printStackTrace();
		}
		catch (IOException e) {
			e.printStackTrace();
		}
		finally {
			try {
				in.close();
				httpConn.disconnect();
			}
			catch (Exception ex) {
				ex.printStackTrace();
			}
		}

		// 出现异常则返回空
		return null;
	}

	/**
	 * 使用正则表达式解析返回的HTML文本,得到本机外网地址
	 * @param html
	 */
	private void parse(String html) {
		Pattern pattern = Pattern.compile("(\\d{1,3})[.](\\d{1,3})[.](\\d{1,3})[.](\\d{1,3})", Pattern.CASE_INSENSITIVE);
		Matcher matcher = pattern.matcher(html);
		while (matcher.find()) {
			myExternalIpAddress = matcher.group(0);
		}
	}

	/**
	 * 得到本机外网地址,得不到则为空
	 * @return
	 */
	public String getMyExternalIpAddress() {
		return myExternalIpAddress;
	}

	public static void main(String[] args) {
		ExternalIpAddressFetcher fetcher = new ExternalIpAddressFetcher("http://checkip.dyndns.org/");

		System.out.println(fetcher.getMyExternalIpAddress());
	}
}